The brake lights of the vehicle turn on as normal because the brake pedal contacts a switch called a brake light switch. On some vehicles, this switch may be incorrectly programmed to allow the brake lights to stay on continually. Secondly, each tire has a sensor in it that actively measures the air pressure that the tire contains. When this pressure becomes too low, the tire pressure warning light comes on. In some cases, the threshold of when the warning illuminates is too low.